Phoronix was kind enough to add a deliciously lengthy nine-page compare and contrast between FreeBSD 8 and Ubuntu 9.10 to their arsenal of articles. "Canonical will be releasing Ubuntu 9.10 at the end of next month while the final release of FreeBSD 8.0 is also expected within the next few weeks. With these two popular free software operating systems both having major updates coming out at around the same time, we decided it warranted some early benchmarking as we see how the FreeBSD 8.0 and Ubuntu 9.10 performance compares. For looking more at the FreeBSD performance we also have included test results from FreeBSD 7.2, the current stable release. In this article are mostly the server and workstation oriented benchmarks with the testing being carried out on a dual AMD Opteron quad-core workstation."

from /usr/src/UPDATING:
NOTE TO PEOPLE WHO THINK THAT FreeBSD 8.x IS SLOW:
FreeBSD 8.x has many debugging features turned on, in
both the kernel and userland. These features attempt to detect
incorrect use of system primitives, and encourage loud failure
through extra sanity checking and fail stop semantics. They
also substantially impact system performance. If you want to
do performance measurement, benchmarking, and optimization,
you'll want to turn them off. This includes various WITNESS-
related kernel options, INVARIANTS, malloc debugging flags
in userland, and various verbose features in the kernel. Many
developers choose to disable these features on build machines
to maximize performance. (To disable malloc debugging, run
ln -s aj /etc/malloc.conf.)

Unfortunately Phoronix neglected to publish the kernelconfig they used and also how you compile your software is up to you. So if you like to use a newer gcc on FreeBSD for your ports you are free to do so..